JPH09130169A - Converter for converting single-ended input into differential output signal, method for generating differential output signal dependently on input, and converter for converting differential input voltage into single-ended output voltage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce in phase input requirement without causing excess power consumption and without increasing the complexity of components by changing precisely a resistance rate of input and feedback resistors. SOLUTION: The converter includes a complete differential amplifier whose one input terminal is coupled with a single end input and the other input terminal is coupled with a point of a fixed voltage (e.g. AGND). The converter includes a 1st receiver R1 connected between the single end input and a noninverting input terminal of the complete differential amplifier, a 2nd resistor R2 connected between a point of a fixed voltage (e.g. AGND) and an inverting input terminal of the complete differential amplifier, a 3rd resistor R3 coupled between the noninverting input terminal and the inverting input terminal of the complete differential amplifier, and a 4th resistor R4 coupled between the inverting input terminal and the noninverting input terminal. Then the resistance is selected by a relation of R3 /R1 ≠R4 /R2 .

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to differential amplifier circuits, and more particularly to single-ended-to-differential and differential-to-single-ended converters.

[0002]

TECHNICAL BACKGROUND A typical operational amplifier is shown in FIG. As will be readily appreciated by those skilled in the art, the relationship between the output signal and the input signal is commonly expressed as V _OUT / V _in = −R ₃ / R ₁ . The positive input to the amplifier is typically an analog ground ("AGN") midway between the positive and negative supply rails.
Note that it is connected to D "). Amplification is thus defined by the resistivity of R ₃ to R ₁ .

For high dynamic range applications, a differential circuit such as that shown symbolically in FIG. 2 is desired. The need for a differential circuit is simple.
For an input voltage with a peak-to-peak voltage of 2v, the outputs, INP and INM, produce a differential output range of + 2v to -2v, which results in an effective dynamic range of the input signal without increasing the amplifier supply voltage. Doubles. This higher dynamic range in the amplifier is highly desirable in low power audio or voice processing circuits.

FIG. 3 is a circuit diagram of a typical differential amplifier having differential inputs INM and INP and differential outputs OUTP and OUTM. The gain of this circuit is generally represented by equation (a) shown below.

As is commonly known to those skilled in the art, the common mode input voltage V _CM (≡ (V _A + V _B ) / 2)) is fixed and, in the case of a fully differential amplifier, differential. Note that it is independent of input.

A conventional single-ended-differential amplifier is shown in FIG. 4, which results from the combination of FIGS. Note that the input to the amplifier at the positive terminal is now connected to AGND. Since IN is proportional to AGND, the gain of the amplifier of FIG. 4 is also represented by the equation (b) shown later.

However, the common mode input voltage V _CM , that is, (V _A + V _B ) / 2, changes with the input voltage IN in the manner shown by the following equation (c).

[0008]

(Equation 7)

Thus, when IN decreases, V _CM also decreases due to its association with OUTP and vice versa. In practical terms, the common mode input voltage of the differential amplifier in FIG. 4 varies according to the input signal, as opposed to the independence from the differential inputs in the fully differential amplifier of FIG.

This dependence requires a large common mode input range for the single-ended-to-differential amplifier, especially for applications with low supply voltages such as 2.7v. The large common mode input voltage forces the transistors used for the tail currents of the differential pair to operate in the linear region instead of the strong inversion region.
Therefore, conventional single-ended-to-differential amplifiers require complementary input stages to handle large common mode input signals to the amplifier, resulting in extra power and more components. It was

For high dynamic range applications, it is desirable to have a single-ended-differential amplifier with low common mode input requirements without incurring extra power consumption or increasing component complexity.

[0012]

SUMMARY OF THE INVENTION An improved single-ended-to-differential converter with reduced common mode input requirements is disclosed. By accurately changing the resistivities for the input and feedback resistors, the input common mode ratio can be lowered to any desired value. Specifically, the common mode input voltage causes the ratio of the feedback resistor to the input resistor connected to a fixed voltage (eg, AGND) to be much greater than the corresponding ratio between the resistors connected to the input signal. Can be lowered.

In accordance with the present invention, a converter is disclosed for converting a single-ended input V _IN to a differential output signal V _OUT via positive and negative output terminals. The converter includes a fully differential amplifier with one of its input terminals coupled to a single-ended input and the other input terminal coupled to a fixed voltage (eg, AGND). The converter also includes a first terminal coupled between the single-ended input and the positive input terminal of the fully differential amplifier.
Resistor ("R ₁ "), fixed voltage (eg AGND)
A second resistor (“R ₂ ”) coupled between the positive input terminal and the negative output terminal of the fully differential amplifier, and a _second resistor (“R ₂ ”) coupled between the positive input terminal and the negative output terminal of the fully differential amplifier. 3 resistors ("R
₃ "), and a fourth resistor (" R ₄ ") coupled between the negative input terminal and the positive output terminal, the value of such resistor being R ₃ / R ₁ ≠ R Governed by ₄ / R ₂ .

The same principles can be applied to differential-to-single-ended converters. Further objects, features and advantages of the invention will be apparent to those skilled in the art from the detailed description that follows.

[0015]

Detailed Description of the Preferred Embodiment Single Termination According to the Invention-
Reference is made to FIG. 5, where a circuit diagram of a differential amplifier is shown. The input resistor is represented as R ₁ and the feedback resistor R
₃ is coupled between the output OUTM and the positive terminal of the amplifier. Another feed resistor R ₄ is coupled between the output OUTP and the negative terminal of the amplifier, while the input resistor R 4
₂ is coupled between the negative terminal and AGND.

To address the problem of common mode input requirements in conventional single-ended-differential amplifiers, resistors R ₁ , R ₂ , R.
₃ and R ₄ are set so that their conventional symmetry as in FIG. 4 is removed and R ₃ / R ₁ ≠ R ₄ / R ₂ .

Furthermore, in order to reduce the requirement for the common mode input of the single- _ended- differential amplifier, the resistors R ₁ , R ₂ , R ₃ and R are used.
The value of ₄ can be adjusted according to the combined relationships shown below. (Assuming infinite amplifier gain)

[0018]

(Equation 8)

Where V _CM is the common mode voltage at the input of the amplifier. With Equations 1 and 2 in mind, the goal is then to minimize Equation 2 while retaining the desired gain according to Equation 1.

For example, for a conventional amplifier, R_Three
Is R₁Is twice that of R_FourIs R_TwoThat's twice as much
ChiR_Three/ R₁= R_Four/ R_TwoIt is. This ever needed
However, the requirement for in-phase input is
To increase conventional single-ended-to-differential amplifier,
Is not completely non-operational for low-end applications,
It has become more complicated. In-phase input request, ie
V_cm/ V_INRatio R to reduce the ratio_Three/ R₁Is equation 2
As you can see in R_Four/ R_TwoMuch bigger than
Need to be Also, to satisfy Equation 1, R_ThreeIs
Large R_Four/ R _TwoR to compensate the gain as a result of₁
Is almost the same as.

As will be appreciated by those skilled in the art, the same principles of relaxing the common mode input requirements for single-ended-to-differential converters can be applied to differential-to-single-ended converters as shown in FIG. it can.

In FIG. 6, the differential input signal V _IN has its positive terminal INP connected to the positive terminal of the amplifier via the input resistor R ₁ and the negative terminal INM via the input resistor R _2. Connected to the negative terminal of the amplifier. Feedback resistor R ₃ is coupled at node B between the output terminal and the positive terminal. Another resistor R ₄ is coupled between the negative terminal and a fixed voltage (eg AGND).

In this case, the resistors R ₁ , R ₂ , R ₃ and R ₄ are governed according to the following equation:

[0024]

(Equation 9)

While only a few exemplary embodiments have been described in detail above, many variations will be apparent to those skilled in the art without substantially departing from the novel teachings and advantages of the invention. It will be readily appreciated that this is possible in the examples. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the appended claims. In the claims, the means-plus-function clause is intended to encompass structures described herein as performing the described functions, and not only structural equivalents but also equivalent structures. To be done. That is, nails and screws may not be structurally equivalent in that nails use cylindrical surfaces to secure wooden parts together while screws use helical surfaces. Although not, it is possible that nails and screws could be equivalent structures in an environment that secures wooden parts.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional amplifier.

FIG. 2 is a diagram showing a single-ended-differential amplifier by a symbol.

FIG. 3 shows a conventional fully differential amplifier.

FIG. 4 shows a conventional approach to a single-ended-differential amplifier.

FIG. 5 shows a single-ended-differential amplifier according to the present invention.

FIG. 6 illustrates a differential-to-single-ended converter also in accordance with the present invention.

[Explanation of symbols]

R ₁ input resistor R ₂ input resistor R ₃ feedback resistor R ₄ feedback resistor V _IN differential input signal V _OUT differential output signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Darius Shamrow United States, 92677 California, Laguna Niger, Bell Maison, 30756 (72) Inventor Cassif A Amed United States, 92715 Irvine, California, Parkview Lane, 3701, Apartment 11-Di (72) Inventor Gunmin Inn United States, 92715 Parkview Lane, Irvine, California, 3900, Apartment 6Sii

Claims (8)

[Claims] 1. Single-ended input V_INThe positive and negative output terminals
Differential output signal V via_OUTConvert to convert to
One of its input terminals is coupled to the single-ended input.
, The other input terminal is connected to a predetermined fixed voltage.
Including a fully differential amplifier that is
The width device has a predetermined common-mode voltage V_cmAnd further
A single-ended input and the positive input terminal of the fully differential amplifier
A first resistor means ("R₁)) Of the fully fixed differential amplifier with the predetermined fixed voltage
Second resistor means coupled between the negative input terminal
("R_Two)), The positive input terminal and the negative output terminal of the fully differential amplifier
A third resistor means ("R_Three")
And a first coupling coupled between the negative input terminal and the positive output terminal.
4 resistor means ("R _Four)) And where R_Three/ R
₁≠ R_Four/ R_TwoIs a converter. 2. The converter has the following equation: And having a gain factor of the single-ended input V _IN to the differential output V _OUT determined by
The following formula [Formula 2] 2. A voltage transfer function of the single-ended input V _{IN to} the predetermined common mode voltage V _CM determined by
Converter described in. 3. The converter of claim 1, wherein the predetermined fixed voltage is midway between a positive power supply voltage source and a negative power supply voltage source. 4. Input V_INDifferential output signal V_OUTDepart
(A) One of the input terminals has the input V_INIs bound to
The other input terminal to a predetermined fixed voltage.
The input V to a fully differential amplifier that is coupled _INgive
And the fully differential amplifier has a predetermined
Common-mode voltage V _cmAnd (b) the single-ended input and the fully differential amplifier
The first resistor (“R₁))
(C) the predetermined fixed voltage and the fully differential
A second resistor between the negative input terminal of the amplifier
("R_Two)), And (d) the positive input terminal of the fully differential amplifier and the
A third resistor (“R_Three))
And (e) a fourth terminal between the negative input terminal and the positive output terminal.
Resistor ("R_Four)), And (f) the R₁, R_Two, R_Three, And R_FourThe value of
These values are R_Three/ R₁≠ R_Four/ R_TwoWill obey
A method comprising: 5. (g) The following equation (3) The single-ended input V _IN to the differential output V
Based on the gain ratio of _OUT and the following formula Adjusting the values of the R ₁ , R ₂ , R ₃ and R ₄ of the converter based on the voltage transfer function of the single-ended input V _{IN to} the predetermined common mode voltage V _CM determined by The converter of claim 4, further comprising: 6. The converter of claim 4, wherein the predetermined fixed voltage is midway between a positive power supply voltage source and a negative power supply voltage source. 7. A converter for converting a differential input voltage V _IN to a single-ended output voltage V _OUT via positive and negative output terminals when V _IN = INP-INM, the input terminal One is connected to the positive input INP,
A fully differential amplifier having its other input terminal coupled to the negative input INM, said fully differential amplifier having a predetermined common mode voltage V _CM , and further comprising said INP and said fully differential amplifier. A first resistor means ("R ₁ ") coupled to the positive input terminal of the second resistor and a second resistor coupled to the negative input terminal of the INM and the fully differential amplifier. Means ("R ₂ "), a third resistor means ("R ₃ ") coupled between the positive input terminal and the output, and a third resistor means ("R ₃ ") coupled between the negative input terminal and a fixed voltage. And a fourth resistor means (“R ₄ ”), where R ₃ / R ₁ ≠ R
_A converter that is ₄ / R ₂ . 8. The converter has the following equation: The converter also has a ratio of the gain of the differential input voltage V _IN to the output voltage V _{OUT given} by: 8. The converter of claim 7 also having a voltage transfer function of the differential input V _{IN to} the predetermined common mode voltage V _CM determined by: